Experiments in progress include: 1) Study of cell population dynamics in rat taste buds. Autoradiographic studies using 3H-Thymidine labelling of taste bud cell nuclei will be done to estimate the life span of dark and light cells in vallate and foliate papillae. In a preliminary experiment the life of the dark cell is estimated to be 6-7 days. The life of the light cell is considerably longer. 2) Efferent innervation of the taste bud - Counts of nerve processes on electron micrograph montages of transverse sections through rat fungiform papillae from operated animals suggest the presence of efferent nerves in fungiform papillae. These may be associated with taste buds. Animals were operated as follows: The facial nerve root was cut between the brain stem and its entrance into the facial canal. Ipsilateral lingual nerves were cut. This reduced the population of nerves in fungiform papillae essentially to those afferents arising from cell bodies in the geniculate ganglion. Control animals had only lingual nerve severed. 3) Organ culture of primary olfactory pathway -Preliminary attempts to grow presumptive olfactory epithelium and presumptive olfactory bulb in culture have been successful. These experiments are in progress to study synaptogenesis and appearance of olfactory specific protein. BIBLIOGRAPHIC REFERENCES: Farbman, A.I. and Gesteland, R.C. 1976. Developmental and electrophysiological studies of olfactory mucosa in organ culture. In: V International Symposium on Olfaction and Taste. Eds.: D.A. Denton and J.P. Coghlan. Academic Press, N.Y., pp. 107-110. Baratz, R.S. and Farbman A.I. 1975. Morphogenesis of rat lingual filiform papillae. Am. J. Anat., 143: 283-302.